In organic light emitting diodes (OLEDs), the light generated is only partially output directly.
The rest of the light is distributed in different loss channels, as represented in a representation of an organic light-emitting diode 100 in FIG. 1. FIG. 1 shows an organic light-emitting diode 100 having a glass substrate 102 and, arranged thereon, a transparent first electrode layer 104, for example consisting of indium tin oxide (ITO). Arranged on the first electrode layer 104, there is a first organic layer 106, on which an emitter layer 108 is arranged. A second organic layer 110 is arranged on the emitter layer 108. Furthermore, a second electrode layer 112, for example consisting of a metal, is arranged on the second organic layer 110. An electrical current supply 114 is coupled to the first electrode layer 104 and to the second electrode layer 112, so that an electrical current for generating light is passed through the layer structure arranged between the electrode layers 104, 112. A first arrow 116 symbolizes a transfer of electrical energy into surface plasmons, for the case in which at least one electrode 112, 104 consists of metal. A further loss channel may be seen in absorption losses in the light emission path (symbolized by means of a second arrow 118). Light not output in the desired way from the organic light-emitting diode 100 is, for example, a part of the light which results from reflection of a part of the generated light at the interface of the glass substrate 102 with air (symbolized by means of a third arrow 122) and from reflection of a part of the generated light at the interface between the first electrode layer 104 and the glass substrate 102 (symbolized by means of a fourth arrow 124). The part of the generated light output from the glass substrate 102 is symbolized in FIG. 1 by means of a fifth arrow 120. As can be seen, there are therefore the following loss channels, for example: light loss in the glass substrate 102, light loss in the organic layers and the transparent electrode 104, 106, 108 and 110 and surface plasmons generated on the metal cathode (second electrode layer 112). These light components cannot readily be output from the organic light-emitting diode 100.
To date, there have been two approaches for increasing the light output:    (1) external output; and    (2) internal output.
External output may be understood as meaning that a device is adapted so that it outputs the light from the substrate in emitted light.
Examples of such a device may be:    (a) sheets with scattering particles on the outer side of the substrate;    (b) sheets with surface structures (for example microlenses);    (c) direct structuring of the outer side of the substrate; and    (d) introduction of scattering particles into the glass.
Some of these approaches (for example scattering sheets) are already used in OLED lighting modules, or their capacity for scaling up has been shown.
Inter alia, these approaches for external light output have the following two disadvantages:    (1) the output efficiency is limited to approximately 60 to 70% of the light guided in the substrate.    (2) The appearance of the OLED is substantially influenced. Applied layers or films lead to a milky/diffusely reflective surface.
Internal output can be understood as meaning that a device is adapted so that it outputs the light which is guided in the organics and the transparent electrode. There are several known technological approaches for this, but they are not yet available on the market in OLED products.
Such approaches are, for example:    (1) so-called low-index grids (as described, for example, in Sun and Forrest, Nature Photonics, page 483 ff., 2008; these consist of structured regions including a material with low refractive index, which are applied on the ITO electrode).    (2) highly refractive scatters below an ITO anode in a polymer matrix (as described, for example, in US 2007/0257608 A1). In this case, the polymer matrix generally has a refractive index in a range of n=1.5 (for example at a wavelength of 633 nm) and is usually applied wet-chemically.    (3) So-called Bragg gratings or photonic crystals with periodic diffraction structures having structure sizes in the wavelength range of light (as described, for example, in Ziebarth et al., Adv. Funct. Mat. 14, page 451 ff., 2004; and Do et al., Adv. Mat. 15, page 1214 ff., 2003).
Furthermore, T. Georgiou et al., Graphene bubbles with controllable curvature, Applied Physical Letters, Vol. 99, 2011 describes a method for producing graphene bubbles.